All,
It would be nice of Princess to create a FAQ document discussing timelines. However, we won't hold our breath for that.
Here's what I've experienced so far - feel free to correct me if I'm mistaken.
First, you check in online by using the Princess app or the web version. As part of check-in, you can choose the pick the medallions up at the port or have them mailed. I opted for mail (understanding not all have that option or care to pay for shipping - that's a subject of many other threads). There is no mention of when they will be shipped, and people may wonder... The medallions aren't actually shipped until about 3 weeks from embarkation. I received an email stating it was being shipped, and then I received subsequent emails as the medallions were transported and ultimately delivered (about 5 days for me - from Los Angeles to Phoenix).
At 8 days prior to embarkation, my Princess app magically displayed a barcode (which I assume replaces boarding passes), with instruction to proceed to the Green Lane signs. I am told to have my medallion and travel documents (they don't say what those are; I assume passports) upon arrival.
Hope this helps some who are curious about the "who's, what's, and where's" of their shiny little medallions and how to gain access to the ship on embarkation day.
In summary, medallions are shipped 2 - 3 weeks prior to embarkation; the barcode appears about a week out.
Happy sailing...